In order to get permission to use the song "Your Body is a Wonderland" in this episode, John Mayer asked that he be given a Dundie.
Dwight (Rainn Wilson) holding the microphone for Angela (Angela Kinsey) while she sings "Little Drummer Boy" was not in the original script. Kinsey doesn't enjoy singing in public and got very nervous filming the scene by herself, so during one take Wilson improvised holding the microphone and mimicking the drumbeat to help put her at ease.
Angela bases what color is "whorish" on whatever Phyllis is wearing.
Angela sings "Little Drummer Boy" on the karaoke machine, which is her favorite song. In the pilot episode, Dwight is seen singing that song.
Phyllis Smith improvised her character's running gag of trying to escape Angela's party.